First off, fish ALWAYS seem hungry..i'm not sure why this is, but what you're feeding them now is just fine. The rule is, feed them no more than what they can consume in 5 minutes. If they always move to the top of the tank when someone walks by, it's because fish have routines where they remember where you fed them...ie...if you only fed them on the right side of the tank, they'll start to always go to the right side of the tank. So, when you feed them, you are coming towards the tank and then they get fed....they remember this, so whenever someone walks by..they think they're getting fed.

As for the "fungus", I'm not sure what it would be, but if it seems sick, you should probably remove it from the tank, to avoid passing it on to the other fish.